1. Field of the Invention
The present invention relates to an engine control device having a variable valve timing (VVT) mechanism capable of changing a phase of an intake valve and/or an exhaust valve, and particularly to an engine control device configured to be able to prevent a combustion deterioration, a torque reduction, and the like caused by a mechanical response delay and an overshoot of the variable valve timing mechanism at a transition time such as an acceleration/deceleration time.
2. Background Art
For example, as disclosed in JP Patent Publication (Kokai) No. 8-261026A (1996), conventionally there has been used a variable valve timing mechanism capable of changing a phase of an intake valve and/or an exhaust valve (hereinafter also referred to simply as an intake/exhaust valve) in order to change a degree of overlap between an opening timing of the intake valve and a closing timing of the exhaust valve according to an engine operating state.
In an engine having such a variable valve timing mechanism, generally, an increase in the degree of overlap increases the internal EGR amount, leading to a reduction in charging efficiency; conversely, a reduction in the degree of overlap reduces the internal EGR amount, leading to an increase in charging efficiency. The internal EGR amount and the charging efficiency are closely related to an engine output torque, combustion characteristics, exhaust performance (exhaust emission characteristics), and the like.
Note that the variable valve timing mechanism is configured to change a valve phase by a hydraulic, electric actuator, and other actuator. Therefore, a change in valve phase at a transition time (at least the opening timing of the intake valve and/or the closing timing of the exhaust valve) entails a mechanical response delay (following delay) or an overshoot.
In contrast to this, the ignition timing at a transition time when a change in phase of an intake/exhaust valve is made is set assuming that the phase of the intake/exhaust valve has reached a target phase. If the following delay or overshoot occurs, the ignition timing does not match an optimal ignition timing, leading to a torque reduction or a combustion deterioration (occurrence of knocking or the like).
In order to solve such problems, for example, JP Patent Publication (Kokai) No. 2006-090198A proposes to correct the ignition timing at a transition time in consideration of a change in temperature and pressure inside a combustion chamber with a change in phase of the intake valve.